Hi Mik,

We have not integrated Totara with Shopify. But we have integrated Totara and Magento as well as Totara with Sitecore.

Yes. Shopify can be integrated with Totara. But there is no free/premium plugins available to use.

Shopify and Totara both have a very good APIs. 

We need to create a custom local plugin in Totara that listens to Shopify API requests ( user created, checkout, search course) and do appropriate actions in moodle, as well as expose Moodle events(course created, student enrolled) and call appropriate Shopify API.

We have integrated Sitecore with Totara.

Thanks,
 Charles A.